So I turn on my water tap. In my case, that water started out on top of a mountain, and then it flowed down and went into a reservoir. Then it flowed down a big rock tunnel to Denver, went through a bunch of pipes, and via some sort of magic it comes out of my sink.

At some point in that process, that water got treated, right? Someone had to filter the water bugs out of it and the giardia and stuff. Are there things that a filter can't get out? Or is the problem figuring out what to do with the stuff that gets filtered out?

I've seen simple filtering systems in survival kits that are basically a plastic tent. You let the water evaporate inside it, and it recondenses in the heat on the tent. Then it drips down and you drink it. The stuff that recondenses is presumably two parts hydrogen and one part oxygen. It contains no water bugs or giardia or fracking solutions, and the filtering costs nothing.